1. Technical Field
The present application relates to a drill, such as a twist drill, having a body provided with chip flutes as well as a drill front provided with at least two main cutting edges merging into each other.
2. Background Information
According to standard DIN ISO 5419, such a twist drill comprises a drill tip, herein referred to as drill front, which substantially provides the cutting functionality of the drill. Adjacent to the drill tip, there is a body, into which the chip flutes, extending, in at least one possible embodiment, in helical form and starting each at a main cutting edge of the drill tip, are formed. In the longitudinal direction of the drill, a shaft, by which the drill is chucked and held, is adjacent to the body.
In a conventional twist drill with two main cutting edges, these are arranged relative to each other at an acute angle, as described in DIN 1414-1. The two main cutting edges are connected with each other through a chisel edge arranged in the center of the drill. In the area of the chisel edge, the drill tip has a web thickness. The chisel edge is at the same time the foremost point of the drill, to which the main cutting edges are adjacent in the way of a conical surface, as well as the tool flanks, which are adjacent to the main cutting edges.
The drilling operation of such a twist drill in a workpiece forms a drill hole with a cone-shaped bottom. For certain applications, however, blind holes with a bottom as planar or flat as possible are desired. It is not possible to drill such blind holes by means of a conventional twist drill, due to the inclination of the main cutting edges to each other at an acute angle.
European Patent No. 0 089 123 A1 describes a drill for producing a hole with an almost planar bottom. This drill is provided with a primary edge arranged in the center of the drill and only extending over a partial section of the drill diameter. A secondary edge, set off in the longitudinal direction of the drill, is adjacent to one side, which secondary edge extends from the primary edge to the outer circumference of the drill. Due to the projecting primary cutting edge, this drill is also not able to produce a hole bottom with a completely planar surface. The projecting primary edge is necessary in this case for centering purposes.
Furthermore, German Patent Publication Published for Opposition Purposes No. 1 177 904 describes a slot milling cutter, which is provided on its front face with a total of four front cutting edges, which are, however, not connected with each other over the center of the cutter. Such a milling cutter is, however, not suitable for drilling operations due to the fact that it has no cutting edge in the center area, and thus a purely rotational movement will not remove any chips in the center area. The cutter must, therefore, necessarily be moved in a lateral direction, too.
U.S. Pat. No. 6,135,681 describes a plane-bottom drill with a cutting bit whose main cutting edges extend in a plane which is perpendicular to the longitudinal axis of the drill.